RU2024853C1 - Method of detection of explosives - Google Patents

Abstract

FIELD: distant detection of explosives. SUBSTANCE: tested object is subjected to effect of two linear-frequency-modulated pulses with time intervals τ₁ between them. Average basic frequency is equal to frequency of one transition and deviation which provides excitation of the total line. Then radiofrequency pulse is used for influence in time τ₂ with basic frequency being equal to frequency of the lateral and longitudinal relaxations. Response signal is detected at single pulse frequency. EFFECT: improved reliability; improved efficiency. 5 dwg

Description

 The invention relates to methods for detecting explosives and can be used for remote detection of explosives containing nitrogen nuclei.

 A known method for the detection of explosives, including the impact on the subject with a series of radio frequency pulses and the registration of the response signal, which determines the presence of the desired substance [1].

 The disadvantage of this method is the low sensitivity due to the low intensity of the observed signals. This method allows you to detect explosives at a distance of ≈60 cm

 The closest in technical essence is a method for detecting explosives, which includes a two-frequency exposure of an object to be examined with two linearly-frequency-modulated pulses with an average filling frequency equal to the frequency of one of the transitions and with a deviation providing excitation of the entire line, and one radio-frequency pulse with a filling frequency equal to the frequency of another transition and the registration of the response signal, which judges the presence of the desired substance [2].

 However, this method also has a relatively low sensitivity. They can detect explosives at a distance of ≈1.2 m.

 The objective of the invention is to develop a method for detecting explosives, which allows to increase sensitivity.

When explosives containing nitrogen nuclei are detected, the object under investigation is affected by two linearly-frequency-modulated pulses with an average filling frequency equal to the frequency of one of the transitions and with a deviation providing excitation of the entire line and one radio-frequency pulse with a filling frequency equal to the frequency of the other transition and registration of the response signal, according to which the presence of the desired substance is judged, moreover, they are first exposed to two linearly-frequency-modulated pulses with a time interval ₁ therebetween, and then after a time τ ₂ RF pulse, and registration response signal produced at the frequency of a single pulse, wherein τ ₁ and τ ₂ is set less than the transverse and longitudinal relaxation times.

In FIG. 1 shows a diagram of a quadrupole spin system of ¹⁴ N nuclei; in FIG. 2,3 - pulse programs of excitation of echo signals; in FIG. 4 is a block diagram of a device with which the proposed method is implemented; in FIG. 5 - spectrum of the test substance.

 Consider the excitation of signals by pulse programs in FIG. 2,3.

The first RF field acts on the average frequency ω _{0, + 1} , and the second on the frequency ω _{0, -1} (see Fig. 2).

The first radio frequency field acts on the average frequency ω _{0, -1} , and the second field on the frequency ω _{0, + 1} (see Fig. 3).

 The amplitudes of the observed signals are proportional to the average frequency of the first RF field. The higher this average frequency, the more intense the amplitude of the observed signal.

 A device for implementing the method comprises a programmer 1, a control unit for controlling the driving oscillators, first 3 and second 4 driving oscillators, the first 5 and second 6 gated amplifiers, the first 7 and second 8 broadband power amplifiers, a two-frequency resonant system 9 made in the form of an antenna, preliminary amplifier 10, receiver 11 signals, indicator 12.

 The device operates as follows. Programmer 1 provides the necessary pulse sequence, i.e. allows you to set the necessary pulse durations, their number, time intervals between them, the pulse sequence repetition rate, various pulses for the control unit of the master oscillators, strobe pulses for gated amplifiers, as well as a clock pulse.

Using the control unit of the master oscillators 2, the necessary frequencies ω _{0, + 1} and ω _{0, -1 of the} first 3 and second 4 master oscillators are set, as well as the frequency deviation of the first 3 and second 4 generators depending on the excitation conditions.

The first gated amplifier 5 and the first broadband power amplifier 7 form and provide chirp pulses with the required amplitude. The average fill frequency of the LFM pulses is ω _{0, + 1} . The second gated amplifier 6 and the second wideband power amplifier 8 generates a pulse with the required amplitude and with a filling frequency equal to ω _{0, -1} .

 The impact of radio frequency pulses on the object is carried out using a two-frequency resonant system 9, made in the form of an antenna (from two turns of communication: each turn of communication for its own frequency). The response signal is amplified by preamplifier 10, which is also a signal selector. In the receiver 11, the response is amplified to the required amplitude (if necessary, and accumulates), then fed to the indicator 12, which is made in the form of an audio signaling device.

In FIG. 5 shows the spectrum of the substance on which this method is implemented. The upper frequencies of these lines (frequencies ω _{0, + 1} ) occupy approximately 860 to 900 kHz, and the lower frequencies (ω _{0, -1} ) - 730-810 kHz. Therefore, in case a) the average frequency of filling of the LFM pulses should vary from 850 to 950 kHz, and in case b) the average frequency of filling of LFM pulses should be changed from 720 to 850 kHz. In this case, it is necessary to set the frequency deviation ≈20% of the average filling frequency of the LFM pulses.

The time intervals τ ₁ (between the chirp pulses) and τ ₂ (between the second chirp pulse and a single pulse) set less times for transverse and longitudinal relaxation.

 The proposed method can detect explosives at a distance of 1.2-10 m. This value largely depends on the mass of explosives, filling frequencies of the LFM pulses, radiation power, antenna design, etc.

Claims (1)

A METHOD FOR DETECTING EXPLOSIVES, including two-frequency exposure of an object to be examined with two linearly frequency-modulated pulses with an average filling frequency equal to the frequency of one of the transitions and with a deviation providing excitation of the entire line and one radio frequency pulse with a filling frequency equal to the frequency of another transition, and registration of the response signal, which judges the presence of the desired substance, characterized in that it is first exposed to two linearly frequency-modulated pulses with TERM interval τ ₁ between them, then after a time τ ₂ - rf pulse, and registration response signal produced at the frequency of a single pulse, wherein τ ₁ and τ ₂ is set shorter than the longitudinal and transverse relaxation times, respectively.

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